rpm sweet spot on class A with 365hp v10 for mpg?

Lowest is best for fuel economy in the V10, but that depends on terrain. Keeping it a little faster, so it doesn't downshift on rolling hills will net better economy than going slow enough it has to downshift constantly.

I do highly recommend a tuner from 5-star. Their tunes will help it climb in OD more often, and not be as "shifty".